The separation of water from organic compounds has been a ongoing challenge for the chemical industry. Typically, techniques such as distillation, decantation, extraction, pervaporation, and chromatography have been employed. These methods, however, often are energy intensive, expensive to operate, and may not be practical or economical for the recovery and purification of materials from dilute aqueous solutions. For example, chemical products such as glucose, which is isolated from biomass, and fermentation products such as lactic acid, phenylalanine, citric acid, L-amino acids, succinic acid, and ascorbic acid, typically must be separated, recovered, and purified from dilute aqueous solutions or fermentation broths. The recovery costs for such fermentation processes are often the major factor which determines their commercial success. The presence of water in chemical products also often complicates purification methods such as crystallization, waste disposal methods, such as incineration, and the recovery and recycling of solvents.
Adsorption from the liquid phase has been disclosed as a method to recover and purify carboxylic acids from dilute aqueous process streams. A variety of carboxylic acids and adsorbents have been reported. For example, European Patent No. 0 324 210 B1 and U.S. Pat. Nos. 4,323,702; 4,720,579; 4,851,573; 4,851,574; and 6,153,791 disclose methods of recovering carboxylic acids or carboxylate salts by adsorption with a polymeric adsorbent resins. Typical resins that have been used as adsorbents are neutral, cross-linked polystyrene polymers, nonionic hydrophobic polyacrylic ester polymers, weakly basic anion exchange resins possessing tertiary amine or pyridine functional groups, and strongly basic anion exchange resins possessing quaternary amine functional groups. The carboxylic acid, generally, is adsorbed on the polymeric adsorbent and then desorbed. The pH of the feed stream may be adjusted to increase the selectivity of the adsorption process. The most common desorbent is water, although solvents such as acetone, ketones, esters, methanol, and ethanol have been used. U.S. Pat. No. 6,153,791, for example, describes a process for the purification of 2-keto-L-gulonic acid by a continuous chromatographic process using a weakly basic ion exchange resin. The adsorbed 2-keto-L-gulonic acid may be desorbed with water or a lower alcohol, such as methanol or ethanol. Similarly, U.S. Pat. No. 6,146,534 discloses processes utilizing thermally-managed chromatography over solid adsorbents for treating aqueous acids to dewater and recover the acids in an organic solvent such as an alcohol. In another example, U.S. Pat. No. 5,071,560 describes a process for the liquid phase adsorptive separation of phenylalanine from a fermentation broth containing phenylalanine salts, carbohydrates, amino acids and organic acids. The feed is contacted, at a pH of 4.5-6.5, with a hydrophobic polar, porous synthetic adsorbent, such as Amberlite XAD-7, whose functional groups have a dipole moment of 1.6-2.0, to selectively adsorb the phenylalanine onto said adsorbent to the substantial exclusion of the other feed components and recovering phenylalanine by desorbing with water, an alcohol, a ketone or an ester.
Adsorption has been used also to remove the water produced during esterification reactions and thereby shift the reaction equilibrium toward esterification. U.S. Pat. No. 5,405,992 discloses a process for the continuous esterification of at least one alcohol and at least one carboxylic acid to form at least one ester and water with the concurrent separation of the esterification products. The process uses a simulated moving bed in which the adsorbent acts both as a catalyst for esterification and as an adsorbent for at least one of the products. In addition, U.S. Pat. Nos. 6,518,454 and 6,476,239 describe processes for the preparation of esters and for the preparation of ascorbic acid, respectively, in a simulated moving bed reactor.
Also disclosed are adsorptive methods of purifying and recovering glucose and ethanol. For example, a process for the recovery of glucose from an aqueous mixture of glucose and polysaccharides is described in U.S. Pat. No. 4,483,980 using countercurrent and co-current simulated moving beds. The mixture is contacted with an X zeolite containing potassium cations at exchangeable cationic sites and selectively adsorbing glucose in the zeolite. The polysaccharides are removed from the zeolite and the adsorbed glucose recovered by means of a desorbent liquid. U.S. Pat. No. 4,333,740 discloses an absorptive process for separating water from a feed mixture comprising ethanol and water, which comprises contacting the feed mixture with an adsorbent comprising corn meal, selectively adsorbing substantially all of the water to be separated to the substantial exclusion of the ethanol, and thereafter recovering high purity ethanol. The process employs a countercurrent moving bed or simulated moving bed countercurrent flow system.
The known methods for dewatering organic compounds are limited primarily to organic acids and typically utilize a strong charge—charge interaction between the acid and adsorbent, such as ion-exclusion, as the primary separation mechanism. Because such charge—charge interactions are weak or non-existent for neutral organic compounds, these methods are not, in general, applicable for dewatering organic compounds without carboxyl substituents. A dewatering process is needed, therefore, that may be used for broad range organic compounds, avoids the limitations discussed above, and may be operated inexpensively on a commercial scale. Such a dewatering process would find commerical application within the chemical and pharmaceutical industries where there is strong interest in the development of water-based fermentation and enzymatic processes.